Not Exactly Rocket Science

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Blogging on Peer-Reviewed ResearchThe plague, or the Black Death, is caused by a microbe called Yersinia pestis. In the 14th century, this microscopic enemy killed off a third of Europe’s population. While many people consign the plague to centuries past, this attitude is a complacent one. Outbreaks have happened in Asia and Africa over the last decade and the plague is now recognised as a re-emerging disease. In 1996, two drug-resistant strains of plague were isolated from Madagascar. One of these, was completely resistant to all the drugs that are used to control outbreaks.

i-841f493708d3928127968efcdc91fed0-yersinia_pestis_fluorescent.jpgAnyone interested in bacteria can attest to their ability to evolve resistance to drugs. In the case of drug-resistant plague, the secret to its powers is a plasmid – a small free-floating ring of DNA, that carries drug resistance genes. Bacteria can trade plasmids across individuals, transferring genes between each other in ways that humans can only achieve with technology. The worry is that common and less harmful bacteria could transfer drug-resistance plasmids over to Yersinia, resulting in new resistant strains.

Timothy Welch and colleagues from the United States Department of Agriculture showed that this concern is well-founded. They found that the plague plasmid is virtually identical in parts to plasmids from an increasingly common strain of Salmonella that is also resistant to multiple drugs. They even found related plasmids were in other drug-resistant bacteria isolated from meat samples across the USA during quality control checks.

i-12096ec9b5ae9084ba2188fef09de864-715px-salmonellaniaid.jpgA word of caution – this doesn’t mean that people risk contracting plague from eating meat. Even though the plasmids are strikingly similar, the bacteria involved are very different. But it does mean that the plague bacterium could potentially gain drug resistance from other common resistant bacteria, if they should both find themselves in the same human or flea host.

Despite this scary scenario, Welch’s study also provides us with a silver lining. We are aware of the threat and we know how to monitor for it, by searching for the plasmid. Monitoring is especially important because the plague has all the qualities you would look for in a potential biological weapon – a high fatality rate, no vaccine and possible air-borne transmission. If the worst happens, we will want to be prepared.

Reference: Timothy J. Welch, W. Florian Fricke, Patrick F. McDermott, David G. White, Marie-Laure Rosso, David A. Rasko, Mark K. Mammel, Mark Eppinger, M.J. Rosovitz, David Wagner, Lila Rahalison, J. Eugene LeClerc, Jeffrey M. Hinshaw, Luther E. Lindler, Thomas A. Cebula, Elisabeth Carniel, Jacques Ravel, Joseph Petrosino (2007). Multiple Antimicrobial Resistance in Plague: An Emerging Public Health Risk PLoS ONE, 2 (3) DOI: 10.1371/journal.pone.0000309

Comments

  1. #1 Robert V Sobczak
    October 23, 2008

    Anytime one goes under surgery, they are put under the risk of those super bugs, and its a race that we are losing as you say. You’d think we’d win with our bigger brains, … but sadly, we are vastly outnumbered. And what’s that saying about kids: they don’t outsmart you because they are smarter, they just have more time. That also applies in this case.

  2. #2 Ned Bedinger
    January 6, 2009

    Back when we still used to think of drug resistance as a feature conferred to pathogenic bacteria by genetic mutation, I was a student attending a meeting of the World Aquaculture Association, and that is where I first heard of plasmid transfer. A scientist presented us with a report on current ocean ecology research, and described evidence of plasmid transfer in the study of a marine garbage dumping site where NYC’s medical waste was being dumped. Especially troublesome was the location of the waste in the study–it was from an offshore dumping site some 100 miles off the coast of New Jersey, USA. As it happened, NYC garbage included medical waste, and was routinely towed on barges to the ocean site and dumped, with the expectation that, because the site was on the outer edge of the continental shelf, all the dumped garbage would sink into submarine canyons and never be seen or heard from again.

    When med waste (syringes, etc) started washing up on the New Jersey shore, it looked bad and there were outcries from the environmental community about ocean dumping of med waste. But when the information about plasmid transfer in ocean dumping sites reached our ears, I think we all caught a glimpse of something truly horrifying: When we dumped medical waste into the sea, we were creating an enhanced evolution laboratory where pathogens were being given unprecedented opportunities, far greater than nature and evolution alone could ever design, to reinvent themselves as super diseases.

    That was 20+ years ago. I have been reminded about the strange brew we’ve made of the oceans every time I hear a report about unaccountable marine mammal deaths and behaviors resembling suicide by self-stranding. About 15 years ago, I myself contracted cellulitis (an infection in the fluid space between the cells, very difficult to identify the pathogen) after only a few minutes standing in the water at an urban boat launch ramp on Puget Sound. Coincidentally, a family friend who had recently moved to a beach house in Southern California contracted “flesh eating bacteria”, and was in a dire condition of illness and convalescence for years afterwards.

    Ed’s report on drug-resistant pathogens reminds me of these things. They haven’t been enough to drive me away from the marine environment, but I try hard to stay out of the water until I am far from urban areas, and to be sure I don’t have any open cuts, scrapes, or even athlete’s foot, before I step in. I would cross an ocean to avoid a marine dumping sites, even though I believe that medical waste is now incinerated instead of dumped.

    Thanks, Ed. Your topic is a sign of the times, and something we all need to be considering while we rethink and re-engineer modern life to be greener, healthier, and more sustainable.

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